Typically, the optical systems used in the context of fabricating microelectronic devices such as semiconductor devices include a plurality of optical elements, such as lenses and mirrors etc., in the light path of the optical system. Those optical elements usually cooperate in an exposure process to transfer an image formed on a mask, reticle or the like onto a substrate such as a wafer. The optical elements are usually combined in one or more functionally distinct optical element groups. These distinct optical element groups may be held by distinct optical element units.
Optical element groups including at least mainly refractive optical elements, such as lenses, mostly have a straight common axis of symmetry of the optical elements usually referred to as the optical axis. Moreover, the optical element units holding such optical element groups often have an elongated substantially tubular design due to which they are typically referred to as lens barrels.